Method of unloading caustic



Jan- 28, 1941. F. R. ELMORE n 2,229,695

METHOD 0F UNLOADING' `('.USTIC Filed 001;. 20, 1939 vIhn/Elvl'cni FRANKR. EIMQRE BY (gpwwqf Awww lil Patented Jan. 28, 1941 UNITED STATESPATENT OFFICE METHOD QF UNLOADING CAUSTIC Application October 20, 1939,Serial No. 300,396

1 Claim.

This invention relates to a method of unloading caustic solutions ofhigh concentration from tank cars or storage tanks and is particularlyrelated to a method of unloading solutions containing 65 to 80 percentby weight of sodium hydroxide. Solutions of this concentration are solidat atmospheric temperatures and in consequence it is the usual practicetto load and unload tank cars used in the shipment of such liquors at anelevated temperature, generally above 150 F., and often at F75-200 F.and to store the unloaded liquor in iron storage tanks. Since suchsolutions are very corrosive at high temperatures they often becomeseriously contaminated with metallic impurities during the unloading andstorage thereof. Thus, it may occur that caustic of high purity whichhas been shipped to its destination in tank cars lined with a protectivecoating may become so contaminated during unloading and storing as to beunacceptable for many purposes.

In accordance with my invention, I have found that tank car or othertanks containing 65-80 percent'sodium hydroxide solutions may beunloaded and the sodium hydroxide stored in metallic equipment withoutsubstantial metal pickup. I have found that substantial corrosion of themetallic storage tank or of the unloading equipment and consequentcontamination of the solution may be minimized or eliminated by dilutingthe solution to a concentration below 55 percent by weight, whereuponthe temperature rises materially usually to 20G-250 F. and cooling thediluted liquor to 150 F. or below with suilcient rapidity to prevent anincrease in the metal content in the solution to more than 0.002 percentand preferably not more than 0.001 percent, calculated on the amount ofsodium hydroxide in the solution. In general, the solution should becooled to 150 F. within 10 minutes after the solution is diluted and inmost cases it is desirable to effect this cooling within 3 minutes.After dilution and cooling the caustic may be vstored in metal equipmentwithoutwith the present invention is diagrammatically illustrated.

In this embodiment I may provide a. suitably jacketed cooler 4, to whichis connected a mixing chamber or T\ 3, for dilution of the caustic. Inthe normal operation of this device caustic of high concentrationcontaining for example 'l0-75 percent NaOH is removed from a tank car(not shown) at a temperature above 180 F.

v and isintroduced into the system through inlet pipe I. Suflicientwaterto dilute the solution to below 55 percentNaOH is introduced into pipe2,` and is mixed with the caustic in the mixing T 3, 4whereupon thetemperature of the solution rises to a temperature well above .200 F.due to theheat of dilution. The caustic passes through the coolercountercurrently to cooling water introduced into water conduit 5, andthe rates of flow of caustic and water are adjusted so that thetemperature of the caustic solution emerging from the cooler throughpipe 6, is not in excess of 150 F. and that the caustic does not remainat a temperature above 150 F. for a period substantially longer thanminutes after dilution of the solution. The cooled caustic is thendischarged into metallic storage tanks not shown.

The rate of introductionof the caustic into the cooler is dependent uponthe cooling capacity of the cooler and the temperature of the coolingwater. Water cooled to about 32 F. is generally satisfactory. It isfound that by eiecting the cooling rapidly, generally within a period ofnot more than 10 minutes and preferably about A 3 minutes afterdilution, no substantial contami- Thus, caustic connation of the causticoccurs. taining 0.0002 percent iron on the anhydrous basis may beunloaded, diluted and stored in iron certain embodiments thereof, it isnot intended.v

that such details shall be regarded as limitations upon the scope of theinvention except insofar as included in the accompanying claim.

I claim:

A method of diluting an aqueous solution ofr sodium hydroxide whichcontains about l0 to 75 percent of sodium hydroxide and not more than0.001 percent iron which comprises diluting the solution while in liquidstate to a concen-j tration` below about 55 percent concentration andcooling the diluted solution to below 150 F., within 3 minutes after thesolution is diluted.

F. R. ELMORE.

